It is believed that presbyopia occurs as a person ages when the lens of the eye loses its elasticity, eventually resulting in the eye losing the ability to focus at near distances, such as the normal reading distance, and in some cases at intermediate distances. Presbyopic persons (presbyopes) complain of difficulty performing close tasks. To compensate for presbyopia, ophthalmic lenses are required to be more positively powered or less negatively powered than ophthalmic lenses for the distance correction. Some presbyopic persons have both near vision and far vision defects, requiring segmented bifocal or multifocal lenses or progressive multifocal lenses, instead of single vision lenses, to properly correct their vision.
Large populations of presbyopes also have an astigmatic refractive error. Astigmatism is optical power meridian-dependent refractive error in an eye. This is usually due to one or more refractive surfaces, most commonly the anterior cornea, having a toroidal shape. It may also be due to one or more surfaces being transversely displaced or tilted. Astigmatism is usually regular, which means that the principal (maximum and minimum power) meridians are perpendicular to each other. People with astigmatism have blurred vision at all distances, although this may be worse at distance or near, depending on the type of astigmatism. These people may complain of sore eyes and headaches associated with demanding visual tasks. Astigmatism can be corrected with an astigmatic ophthalmic lens, which usually has one spherical surface and one toroidal (cylindrical) surface.
Myopia and hyperopia, as well as astigmatism, are caused by low order (defocus and astigmatism) and high order aberrations of the eye's optics or incorrect axial length, while presbyopia is caused by loss of elasticity of the crystalline lens on the eye.
Approaches to correct the problem of aberrations in the eye are traditionally exclusive from the approaches for correcting the problem of loss of accommodation in the crystalline lens. The approach to vision correction is to measure and to compensate for only defocus (power) and astigmatism (pupil azimuthal angle dependent power), which cause myopia and astigmatism respectively. Presbyopia is typically treated separately. Aberrations have not been used or considered when correcting the presbyopia. The present invention presents a novel approach for designing and manufacturing lenses for correcting presbyopia through use of aberrations.